The invention relates to the use of modified olefin polymers based on modified propylene polymers for producing polyolefin products with simultaneously high requirements for toughness and strength and heat resistance.
Polyolefin products based on propylene polymers with good toughness properties are known.
The toughness of products made of propylene polymers can be improved by using polypropylene blends which comprise elastomers, such as polyisobutylene (Martucelli, E., Polymer 24(1983), 1458), ethylene-vinyl acetate copolymers [Thomas, S., Kautschuk-Gummi-Kunststoffe (Rubbers and Plastics) 40(1987), 665-671 EPR [Greco, R., Polymer 28(1987), 1929-1936], EPDM [Karger-Kocsis, J., Polymer 23(1982), 699-705] or copolymers made of ethylene and of higher xcex1-olefins [Yu, T., SPE-ANTEC""94, 2439-2442]. The disadvantage of these melt blends is a loss of strength and heat resistance with increasing elastomer content.
It is known to improve the strength and heat resistance in PP/EPDM blends by irradiation with electrons [Gisbergen, J., Polymer 30(1989)12, 2153-2157] or in PP/EVA blends [Thomas, S., Kautschuk-Gummi-Kunststoffe 40(1987), 665-671] and, respectively, in blends made of polypropylene and ethylene-propylene rubber (U.S. Pat. No. 5,459,201) by kneading in the presence of peroxides.
It is also known to react ethylene polymers, propylene polymers, such as propylene homopolymers or elastomeric propylene-ethylene copolymers or mixtures of these, with bifunctionally ethylenically unsaturated compounds, such as isoprene, in the presence of peroxides in the melt (EP-A1-0 874 009).
Impact-modified blends made of polypropylene, of propylene copolymers with ethylene and/or of higher xcex1-olefins and of elastomeric copolymers made of ethylene and propylene and/or of higher xcex1-olefins, which are prepared by multistage polymerization, are also known (EP-A1-0 680 980; EP-A1-0 942 020).
Polyolefin products with simultaneously high requirements for toughness and strength and heat resistance have until now required the addition of large amounts of additives (e.g. 10% by weight of talc as filler or reinforcing material) to establish the required mechanical properties.
The object of the present invention is to provide polyolefin products which satisfy the requirement profile described above and do so using, in order to establish the required mechanical properties, an amount of additives reduced compared with that used in the prior art.
According to the invention, this object is then achieved by using modified olefin polymers based on modified propylene polymers which olefin polymers have melt indices of from 8 to 100 g/10 min at 230xc2x0 C./2.16 kp and are obtainable by activating a polyolefin composition comprising
X % by weight of a semicrystalline propylene homopolymer and/or of a semicrystalline copolymer made of from 88 to 99.5% by weight of propylene and from 12 to 0.5% by weight of ethylene and/or an xcex1-olefin of the general formula CH2xe2x95x90CHR, where R is a linear or branched alkyl radical having from 2 to 8 carbon atoms, (100-X) % by weight of an elastic copolymer made of from 20 to 70% by weight of ethylene and from 80 to 30% by weight of propylene and/or an xcex1-olefin of the general formula CH2xe2x95x90CHR1, where R1 is a linear or branched alkyl radical having from 2 to 8 carbon atoms,
at elevated temperature with peroxides and reacting the activated polyolefin composition with 0.1 to 10% by weight, based on the polyolefin composition, of volatile bifunctional monomers,
for the production of polyolefin products with simultaneously high requirements for toughness and strength and heat resistance and having the following combinations of properties
KM1, KR1, ZM1, WF1 or
KM2, KR2, ZM2, WF2 or
KM3, KR3, ZM3, WF3 where
KM1xe2x89xa750, KR1xe2x89xa750, ZM1xe2x89xa7350, WF1xe2x89xa7120 and
KM2xe2x89xa725, KR2xe2x89xa740, ZM2xe2x89xa7700, WF2xe2x89xa7135 and
KM3xe2x89xa710, KR3xe2x89xa730, ZM3xe2x89xa71000, WF3xe2x89xa7145 and where
KM is Charpy impact strength at xe2x88x9220xc2x0 C. (kJ/m2) to DIN 53453
KR is Charpy impact strength at +23xc2x0 C. (kJ/m2) to DIN 53453
ZM is tensile modulus at 23xc2x0 C. (MPa) to DIN 53457/ISO 527
WF is Vicat A softening point (xc2x0 C.) to ISO 306,
and where X takes the values
X1=from 60 to 70 for the combination of properties KM1, KR1, ZM1, WF1;
X2=from 70 to 78 for the combination of properties KM2, KR2, ZM2, WF2,
X3 from 78 to 85 for the combination of properties KM3, KR3, ZM3, WF3.
Surprisingly, it has been found that mixtures made of semicrystalline propylene polymers and of elastomeric ethylene copolymers in defined mixing ratios, which have been modified by reacting with bifunctional monomers in the presence of free-radical generators, are suitable for the polyolefin products with high requirements for toughness, strength and heat resistance.
In this specification the terms xe2x80x9cbifunctional monomersxe2x80x9d and xe2x80x9cbifunctionally unsaturated monomersxe2x80x9d have the same meaning, i.e. monomers having (at least) two double bonds.
The novel polyolefin products are preferably produced using modified olefin polymers prepared by
a) mixing the polyolefin composition, which is in a particulate shape, with from 0.05 to 3% by weight, based on the polyolefin composition used, of acyl peroxides, alkyl peroxides, hydroperoxides, peresters and/or peroxycarbonates as free-radical generators capable of thermal decomposition, if desired diluted with inert solvents, with heating to 30-100xc2x0 C.,
b) sorption of volatile bifunctional monomers by the particulate polyolefin composition from the gas phase at a temperature T(xc2x0 C.) of from 20 to 120xc2x0 C., where the amount of the bifunctionally unsaturated monomers is from 0.01 to 10% by weight, based on the polyolefin composition used, and then
c) heating and melting the particulate polyolefin composition in an atmosphere comprising inert gas and/or the volatile bifunctional monomers, and from 110 to 210xc2x0 C., whereupon the free-radical generators capable of thermal decomposition are decomposed and then
d) heating the melt to 220-250xc2x0 C. in order to remove unreacted monomers and decomposition products,
e) pelletizing the melt in a manner known per se.
In another advantageous embodiment, the novel polyolefin products are produced from mixtures made of from 85 to 99% by weight of a modified olefin polymer with a melt index of from 8 to 100 g/10 min at 230xc2x0 C./2.16 kp and from 1 to 15% by weight of an unmodified propylene polymer with a melt index of from 0.5 to 100 g/10 min at 230xc2x0 C./2.16 kp.
It is preferable here for the unmodified propylene polymers to be formed from propylene homopolymers, from copolymers made of propylene with xcex1-olefins having from 2 to 18 carbon atoms, preferably from random propylene copolymers, from propylene block copolymers, from random propylene block copolymers and/or from elastomeric polypropylenes, or from mixtures of the polypropylenes mentioned.
Particularly suitable propylene homopolymers which may, if desired, be present in the novel polyolefin products are propylene homopolymers with bimodal molar mass distribution, weight-average molar masses Mw of from 500,000 to 1,500,000 g/mol, number-average molar masses Mn of from 25,000 to 100,000 g/mol and Mw/Mn values of from 5 to 60, which were prepared in a reactor cascade using Ziegler-Natta catalysts or metallocene catalysts.
In the preparation of the modified olefin polymers present in the polyolefin products it has proven advantageous to modify polyolefin particles directly emerging from the polymerization plant.
It is preferable for the modified olefin polymers to comprise chemically bonded butadiene, isoprene, dimethylbutadiene, divinylbenzene or mixtures of these as bifunctionally unsaturated monomers.
The average sorption time xcfx84s [s] of the volatile bifunctional monomers on the particulate polyolefin composition is advantageously from 10 to 1000 seconds, preferably from 20 to 800 seconds, particularly preferably from 60 to 600 seconds.
It is advantageous moreover for the sorption of the volatile bifunctional monomers by the particulate polyolefin composition to take place from the gas phase during the preparation of the modified olefin polymers at a temperature T(xc2x0 C.) of from 70 to 90xc2x0 C.
The sorbed amount of the bifunctionally unsaturated monomers in the modified olefin polymers is preferably from 0.05 to 2% by weight, based on the polyolefin composition used.
The novel polyolefin products are preferably produced by thermoplastic shaping, in particular by extrusion, injection moulding, blow moulding or thermoforming. Usual processing temperatures for the polyolefin products produced by extrusion, injection moulding or blow moulding are ranges of temperature from 170 to 300xc2x0 C.
Known production processes for blow-moulded polyolefin mouldings are extrusion blow moulding, extrusion stretch blow moulding, injection blow moulding and injection stretch blow moulding (Lee, N., xe2x80x9cPlastic blow molding handbookxe2x80x9d, Van Norstrand Reinhold Publ. New York 1990; Rosato, D., xe2x80x9cBlow molding handbookxe2x80x9d, Carl-Hanser-Verlag Munich 1989).
The injection rate during production of the injection-moulded polyolefin products should be set as high as possible, so that the polyolefin products do not have sink marks or bad flow lines.
In producing the polyolefin products it is preferable to use injection moulding machines with injection units which have three-zone screws with a screw length of from 18 to 24 D.
The polyolefin products which have been produced by extrusion, injection moulding, blow moulding or thermoforming are suitable for use in the packaging industry, in the household equipment industry, in products required in laboratories or in hospitals, in equipment for gardens or agriculture, for transport containers, and also for components in the automotive industry, components of machines and electrical or electronic equipment.
Examples of blow-moulded polyolefin products are bottles, small containers, containers for liquids, liquid-feed parts, air-supply system parts, internal containers, tanks, shock-absorbing components for the automotive industry, folding bellows, protective covers, housings, tubular components, pipes and/or carrying cases.
Examples of injection-moulded polyolefin products are components in the automotive industry, packaging, transport containers, components of machines, of household equipment and of electrical or electronic equipment.
Particularly preferred polyolefin products are shock-absorbing components of motor vehicles, in particular bumpers, spoilers and side edge protection elements.
The following free-radical generators capable of thermal decomposition may be used during the preparation of the modified olefin polymers present in the polyolefin products:
acyl peroxides, such as benzoyl peroxide, 4-chlorobenzoyl peroxide, 3-methoxybenzoyl peroxide and/or methylbenzoyl peroxide;
alkyl peroxides such as allyl tert-butyl peroxide, 2,2-bis(tert-butylperoxybutane), 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, n-butyl 4,4-bis(tert-butylperoxy)valerate, diisopropylaminomethyl tert-amyl peroxide, dimethylaminomethyl tert-amyl peroxide, diethylaminomethyl tert-butyl peroxide, dimethylaminomethyl tert-butyl peroxide, 1,1-di(tert-amylperoxy)cyclohexane, tert-amyl peroxide, tert-butyl cumyl peroxide, tert-butyl peroxide, and/or 1-hydroxybutyl n-butyl peroxide;
peresters and peroxycarbonates, such as butyl peracetate, cumyl peracetate, cumyl perpropionate, cyclohexyl peracetate, di-tert-butyl peradipate, di-tert-butyl perazelate, di-tert-butyl perglutarate, di-tert-butyl perphthalate, di-tert-butyl persebacate, 4-nitrocumyl perpropionate, 1-phenylethyl perbenzoate, phenylethyl nitroperbenzoate, tert-butyl bicyclo[2.2.1]heptanepercarboxylate, tert-butyl 4-carbomethoxyperbutyrate, tert-butyl cyclobutanepercarboxylate, tert-butyl cyclohexylperoxycarboxylate, tert-butyl cyclopentylpercarboxylate, tert-butyl cyclopropanepercarboxylate, tert-butyl dimethylpercinnamate, tert-butyl 2-(2,2-diphenylvinyl)perbenzoate, tert-butyl 4-methoxyperbenzoate, tert-butyl perbenzoate, tert-butyl carboxycyclohexane, tert-butyl pernaphthoate, tert-butylperoxy isopropyl carbonate, tert-butyl pertoluate, tert-butyl 1-phenylcyclopropylpercarboxylate, tert-butyl 2-propylperpenten-2-oate, tert-butyl 1-methylcyclopropylpercarboxylate, tert-butyl 4-nitrophenylperacetate, tert-butyl nitrophenylperoxycarbamate, tert-butyl N-succinimidopercarboxylate, tert-butyl percrotonate, tert-butylpermaleic acid, tert-butyl permethacrylate, tert-butyl peroctoate, tert-butylperoxy isopropyl carbonate, tert-butyl perisobutyrate, tert-butyl peracrylate and/or tert-butyl perpropionate;
and mixtures of these free-radical generators.
Volatile bifunctional monomers which may be used in the preparation of the modified olefin polymers present in the polyolefin products are any bifunctionally unsaturated monomeric compounds which can be sorbed from the gas phase and can be polymerized with the aid of free radicals. Preference is given to the use of the following bifunctionally unsaturated monomers in amounts of from 0.01 to 10% by weight, based on the polyolefin mixture used:
divinyl compounds, such as divinylaniline, m-divinylbenzene, p-divinylbenzene, divinylpentane and/or divinylpropane;
allyl compounds, such as allyl acrylate, allyl methacrylate, allyl methyl maleate and/or allyl vinyl ether;
dienes, such as butadiene, chloroprene, cyclohexadiene, cyclopentadiene, 2,3-dimethylbutadiene, heptadiene, hexadiene, isoprene and/or 1,4-pentadiene;
and mixture of these unsaturated monomers.
Modified olefin polymers preferably present in the polyolefin products are those in which the bifunctionally unsaturated monomer present is chemically bonded butadiene, isoprene, dimethylbutadiene and/or divinylbenzene.
Continuous gas-solid absorbers used for the sorption of the volatile bifunctional monomers in the preparation of the modified olefin polymers are preferably continuous through-flow mixers.
During the preparation of the modified olefin polymers, the heating and melting of the polyolefin particles within which the bifunctionally unsaturated monomers and the acyl peroxides, alkyl peroxides, hydroperoxides, peresters and/or peroxycarbonates have been sorbed as free-radical generators capable of thermal decomposition takes place in an atmosphere of the volatile bifunctionally unsaturated monomers, preferably in continuous kneaders or extruders, with preference in twin-screw extruders.
The modified olefin polymers and, respectively, the mixtures made of modified olefin polymers and of unmodified propylene polymers may comprise, as additives, from 0.01 to 2.5% by weight of stabilizers and/or from 0.1 to 1% by weight of antistats and/or from 0.2 to 3% by weight of pigments and/or from 0.05 to 1% by weight of nucleating agents and/or from 1 to 40% by weight of fillers and/or reinforcing materials and/or from 2 to 20% by weight of flame retardants and/or from 0.01 to 1% by weight of processing aids, based on the modified olefin polymers and, respectively, the mixtures made of modified olefin polymers and of unmodified propylene polymers.
Stabilizers which may be present in the modified olefin polymers or in the mixtures made of modified olefin polymers and of unmodified propylene polymers are preferably mixtures made of from 0.01 to 0.6% by weight of phenolic antioxidants, from 0.01 to 0.6% by weight of free-arylbenzofuranones, from 0.01 to 0.6% by weight of processing stabilizers based on phosphites, from 0.01 to 0.6% by weight of high-temperature stabilizers based on disulphides and on thioethers and/or from 0.01 to 0.8% by weight of sterically hindered amines (HALS).
Suitable phenolic antioxidants are 2-tert-butyl-4,6-dimethylphenol, 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-isoamylphenol, 2,6-di-tert-butyl-4-ethylphenol, 2-tert-butyl-4,6-diisopropylphenol, 2,6-dicyclopentyl-4-methylphenol, 2,6-di-tert-butyl-4-methoxymethylphenol, 2-tert-butyl-4,6-dioctadecylphenol, 2,5-di-tert-butylhydroquinone, 2,6-di-tert-butyl-4-dihexadecyloxyphenol, 2,2xe2x80x2-methylenebis(6-tert-butyl-4-methylphenol), 4,4xe2x80x2-thiobis(6-tert-butyl-2-methylphenol), octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate,1,3,5-trimethyl-2,4,6-tris(3xe2x80x2,5xe2x80x2-di-tert-butyl-4-hydorxybenzyl)benzene and/or pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)]propionate.
A particularly suitable benzofuranone derivative is 5,7-di-tert-butyl-3-(3,4-dimethylphenyl)-3H-benzofuran-2-one.
Particularly suitable HALS compounds are bis-2,2,6,6-tetramethyl-4-piperidyl sebacate and/or poly((6-((1,1,3,3-tetramethylbutyl)amino)-1,3,5-triazine-2,4-diyl)(2, 2,6,6-tetramethyl-4-piperidyl)imino)-1,6-hexanediyl((2,2,6,6-tetramethyl-4-piperidyl)imino))-.
Nucleating agents which may be present in the modified olefin polymers or in the mixtures made of modified olefin polymers and of unmodified propylene polymers are xcex1-nucleating agents, such as talc or sodium methylenebis(2,4-di-tert-butylphenyl)phosphate or xcex2-nucleating agents, such as the dianilide of adipic acid or dibenzoquinacridone or N,Nxe2x80x2-dicyclohexyl-2,6-naphthalenedicarboxamide.
The fillers which may, if desired, be present in the modified olefin polymers or mixtures made of modified olefin polymers and of unmodified propylene polymers are preferably Al2O3, Al(OH)3, barium sulphate, calcium carbonate, glass beads, wood flour, siliceous earth, hollow microbeads, carbon black, talc and/or wollastonite.
The reinforcers which may, if desired, be present in the modified olefin polymers or mixtures made of modified olefin polymers and of unmodified propylene polymers are preferably aramid fibres, cellulose fibres, flax, jute, kenaf, glass fibres, microfibres made of liquid-crystalline polymers and/or polytetrafluoroethylene fibres.
Processing aids which may be present in the modified olefin polymers or in the mixtures made of modified olefin polymers and of unmodified propylene polymers are calcium stearate, magnesium stearate and/or waxes.
The novel polyolefin products preferably have gel contents of from 0.5 to 20% by weight.